1. Field of the Invention
The present invention relates to a multilayer minus filter adopted to separate a light having a narrow wavelength bandwidth by stopping or reflecting the light having the narrow wavelength bandwidth and transmitting other wavelengths, and a fluorescence microscope using the multilayer minus filter.
2. Description of the Related Art
A fluorescence microscope observation is widely used for fundamental research such as medical, dental, pharmaceutical, and biological studies; for testing and research such as clinical health test, animal health, and plant diseases: and for the industrial fields associated with chemicals, pharmaceuticals, semiconductors and the like. Recently, this observation has been an essential technique in the field of genome analysis in molecule biology, and has been more and more important.
A fluorescence microscope is a microscope which determines a substance from an object configuration, or its tone and strength by utilizing fluorescence generated when strong light (excitation light) is emitted to the object. In order to separate the fluorescence, an optical multilayer filter has been widely used conventionally. Because the wavelength of the fluorescence is longer than the wavelength of the excitation light, it has been sufficient if a light (excitation light) having a short wavelength and a light (fluorescence) having a long wavelength can be separated by the conventional optical multilayer filter for use in fluorescence observation.
In contrast, in the recent research of molecule biology, there has been growing need for observing a dynamic behavior of a living cell. Thus, apart from the light for use in excitation or observation of a fluorescence substance, a light for operating a cell (operating light) may be used or a light for stimulating a cell and seeing its reaction (stimulating light) may be used. In such a case, there is a demand for such an optical multilayer filter which cuts the operating light and stimulating light and transmits a light having another wavelength efficiently (hereinafter, referred to as a “minus filter”). In addition, in the similar field, there is a need for simultaneously observing plural kinds of fluorescence lights and precisely observing interaction in cells or layouts of a plurality of observation objects by using lights having a plurality of wavelengths for excitation of a fluorescence substance.
In this case also, there is a demand for such a filter (minus filter) which efficiently transmits both of the wavelengths which are shorter and longer than the excitation light while stopping the excitation light. In the minus filter used in both of these cases as well, the wavelength bandwidth of the lights to be stopped or reflected is often required to be sufficiently narrow.
The conventional minus filters are as follows:
Jpn. Pat. Appln. KOKAI Publication No. 5-215916 discloses a minus filter including a polymeric interference stack in order to protect an eye or other sensors from an undesirable bright light emitted from a light source.
Jpn. Pat. Appln. KOKAI Publication No. 2002-319727 discloses a minus filter using an interference stack formed by alternately laminating dielectric thin films having a small refractive index difference with the same optical thickness (λ/4 when a reflection wavelength is defined as λ) in order to flatten gain spectra of an optical amplifier for use in an optical communication system.
In Jpn. Pat. Appln. KOKAI Publication No. 2003-215332, there is described a minus filter using an interference stack utilizing high order reflection when dielectric thin films are alternately laminated with the same optical thin film for the purpose which is similar to that described in Jpn. Pat. Appln. KOKAI Publication No. 2002-319727.